This invention relates to the formation of fibers from attenuable material and is adapted for use in the formation of fibers from various thermoplastic materials, especially mineral materials such as glass and similar compositions which are rendered molten by heating. Since the equipment or apparatus is especially useful in the attenuation of glass and similar thermoplastic materials, the following description refers to the use of glass by way of illustration.
Certain techniques for utilizing whirling currents or tornadoes for the attenuation of molten glass have been disclosed by us in prior applications above identified, such techniques being identified as toration. For example, U.S. Pat. No. 3,885,940, above identified, and also the companion U.S. Pat. No. 3,874,886, disclose development of pairs of counter-rotating tornadoes by directing a gaseous jet into a larger gaseous blast, thereby creating a zone of interaction including pairs of such tornadoes, and into which zone a stream of molten glass is delivered, with resultant attenuation of the glass stream.
Various different embodiments of equipment for effecting toration are disclosed in various of the applications and patents referred to above, but in all instances a jet or jet flow is caused to penetrate an attenuating blast, the jet being of greater kinetic energy per unit of volume than the blast and having a smaller cross sectional dimension than that of the blast transversely of the blast. In all instances, the stream of attenuable material is introduced into the zone of interaction between the jet and blast either directly under the action of gravity or by initially delivering the stream into the influence of the jet to be carried thereby into the zone of interaction.
In considering the following analysis it is first to be kept in mind that the attenuation of thermoplastic materials such as glass must necessarily take place at an elevated temperature. Thus, the glass is rendered molten by heating, for instance to a temperature above about 1250.degree. C., and for high efficiency the temperature of the attenuating gases in contact with the stream of material and the fiber as it is formed must also be sufficiently high to maintain the glass at an appropriate elevated attenuating temperature.
In certain of the prior applications and patents referred to, for instance in U.S. Pat. No. 3,885,940 both the blast and jet are disclosed as having relatively high temperature, for instance a temperature of the order of 800.degree. C. for the jet and 1580.degree. C. for the blast. Although our prior application Ser. No. 780,589 discloses a method comtemplating the employment of low jet temperatures, for instance a jet temperature of the order of ambient or room temperature, prior application Ser. No. 780,589 discloses blast temperatures at relatively high values such as those referred to above.
The technique of the present invention is in striking contrast to those referred to just above in that the present invention makes possible the use of lower temperatures not only for the jet (as in prior application Ser. No. 780,589), but also for the blast. As the blast embodies relatively large volumes of gas, only a portion of which is actively utilized for the attenuation of each fiber being made, the heating of the entire volume of the blast flow to relatively high temperatures results in substantial heat or energy loss.
The foregoing loss of energy in the known techniques for toration of thermoplastic materials is avoided by the technique of the present invention, according to which provision is made for localized combustion of fuel in the immediate vicinity of the attenuating fiber in the zone of interaction between the jet and blast, so that the desired attenuating temperature may be established and maintained without the necessity for heating the total volume of the blast. In this way the temperature of the gases delivered from the blast generator may be greatly reduced with consequent extensive energy saving.
This technique of the present invention, which may be referred to as "energy localization" not only achieves the desired energy conservation, but in addition this technique affords additional advantages. For example, the technique of the invention provides for rapid cooling of the fibers after attenuation, and with many thermoplastic materials such rapid cooling increases the strength characteristics of the fibers formed. This also maximizes fiber length, which is desirable for most purposes.
Still other advantages are achieved by the technique of the invention, as will appear more fully hereinafter, following description of various of the embodiments of equipment useable according to the technique of the invention.
With the foregoing in mind, attention is directed to the following description of equipment employed according to the invention, as illustrated in the accompanying drawings.